How many direct magnetic courses can there be between two points? Sometimes the answer is three. How many can possibly be right? Actually, all of them.
Mag Course mismatches
I looked at the arrivals into Chicago OHare and noticed something peculiar. Both the BENKY ONE and BRADFORD FIVE arrivals have a transition route from Kirksville VOR (IRK) to LOAMY intersection. But the BENKY arrival shows a course of 068 degrees while the BRADFORD arrival shows 059. I put IRK direct to LOAMY in my GPS ... and got a third course of 064.
Key Takeaways:
- Multiple magnetic courses can be calculated for the exact same two points due to magnetic variation, which is the difference between true and magnetic north and changes over time and location.
- These discrepancies arise from inconsistent applications of magnetic variation: VORs and airports are updated infrequently, charts use different sources (airport vs. VOR), and GPS devices apply it using various manufacturer-specific models.
- Despite these differing displayed magnetic courses, all methods describe the identical ground track, and minor variations are operationally acceptable as GPS units guide pilots directly along the intended path.
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